The RAD52 epistasis group is responsible for repairing the majority of double-stranded DNA breaks via homologous recombination in S. cerevisiae. This group contains at least nine genes: RAD50, RAD51, RAD52, RAD54, RAD55, RAD57, RAD59, MRE11, and XRS2 (1,2). Mutations in many of these genes result in an increased sensitivity to DNA damaging agents, such as ionizing radiation or methylmethanesulfonate, that produce double stranded DNA breaks (3,4). In addition, strains containing mutations in many members of this epistasis group are inviable when the cells go through meiosis, where homologous recombination is required (4,5). While considerable progress has been made toward elucidating the mechanistic steps of and determining the enzymes responsible for homologous recombination in bacteriophage T4 and in E. coli, our current level of understanding of eukaryotic DNA recombination remains limited. The focus of this proposal is to expand our knowledge of this process in S. cerevisiae. Currently, the roles of Rad5l protein, Rad52 protein and RPA are being investigated by the Kowalczykowski group and others. My goal is to use biochemical methods to define the function of the Rad54 protein in homologous recombination. Given the studies to date, I believe that Rad54 protein may have a role either as a DNA chromatin remodeling factor, or as an enzyme capable of stimulating the branch migration phase of homologous recombination. I plan to examine the enzymatic characteristics of Rad54 protein using the bacteriophage T4 and E. coli recombination systems to help guide the initial studies.